The concept that led to propeller propulsion was derived from the rotating screw design, invented by Archimedes in 200 BC. This design was used to lift water from wells and was an inspiration for Leonardo Da Vinci’s flying machine. Although his helicopter-like design was never built, it inspired many aviation innovators. By the mid-1700s, the rotating screw design was also used in marine propulsion.
It wasn’t until the early 1900s that propellers were effectively used for flight. The Wright brothers used their wind tunnel test to study the aerodynamics applied to propeller blades and realized that propellers should be shaped more like a wing than a screw, and that it’s more efficient to add a twist along the length of the propeller blade. Today, propellers come in a vast array of styles that vary in size, shape, material, and application.
Propellers transmit power by converting rotational motion into thrust. They are attached to shafts and receive their energy supply from different types of engines. Once the propeller is spinning, it begins producing forward thrust. This can be explained through Bernoulli’s principle and Newton’s third law of motion. Bernoulli’s principle states that an increase in a fluid’s speed occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. Newton’s third law of motion states that when body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude but opposite in direction of the first body.
Propellers have angled blades because it increases its speed capabilities and requires less force. Propeller blades are twisted because different parts of a propeller move at different speeds. To ensure that they produce a constant thrust at each point, the angle of attack needs to be different along the blade. The pitch, or angle of attack, varies under different scenarios.
Some aircraft— mainly lighter ones— have fixed pitch propellers: the blades are permanently fixed to the hub. Larger and more advanced aircraft have variable pitch propellers which include adjustable pitch propellers, controllable pitch propellers, and constant speed propellers. Adjustable pitch propellers allow the operator to adjust the pitch while grounded. Controllable pitch propellers allow the operator to adjust pitch during flight. Constant speed propellers automatically adjust pitch during flight. One of the benefits of having variable pitch propellers is that they have the ability to feather if an engine fails. This means that the blades are turned edge on, making a shallow angle to oncoming air, which minimizes drag and allows an aircraft to fly on the other engines or glide.
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